. Basic methods for the calibration of sonar equipment. TRANSMITTING RESPONSE H3 kT \ ^r / \ ^ no / / \ / / / lUU 90 5 6 7 8 9 10 20 30 KILOCYCLES PER SECOND 50 60 12. I iansmillini{ chare. Ql! No. 111 transducer vs 3A89 hydrophone (see nni No. 5. Figure 4). TRANSMITTING RESPONSE Transmitting tests are similar to the receiving tests described above. Figure 12 shows the transmitting chart of the projector, using for the sound receiver the same 3A hydrophone standard as in the receiving tests. Reference should be made again lo the log sheet (Figure 4) for the details of this run. This
. Basic methods for the calibration of sonar equipment. TRANSMITTING RESPONSE H3 kT \ ^r / \ ^ no / / \ / / / lUU 90 5 6 7 8 9 10 20 30 KILOCYCLES PER SECOND 50 60 12. I iansmillini{ chare. Ql! No. 111 transducer vs 3A89 hydrophone (see nni No. 5. Figure 4). TRANSMITTING RESPONSE Transmitting tests are similar to the receiving tests described above. Figure 12 shows the transmitting chart of the projector, using for the sound receiver the same 3A hydrophone standard as in the receiving tests. Reference should be made again lo the log sheet (Figure 4) for the details of this run. This log sheet shows that the available power sup- plied to the projector was 160 db vs lO-i" watt (, 1 available watt) from 135 ohms. The log sheet also re- fers to the test circuit used in the transmitting tests. This circuit is reproduced in Figure 13. The receiving amplifier gain given on the log sheet is 4 db, and the testing distance is given as 250 cm. From this information it is possible to compute the transmitting response. This computation is carried through numerically at 25 kc as follows: Chart reading, vs 10 —ic watt in 135-ohni circuit Correction for receiving amplifier gain .... Correction for testing distance: 20 log Correction for available power referied to 1 available + 118db -4db 4-8db Odb Level at hydrophone terminals, vs lO-io watt in 135- ohni circuit -fl22db In order to obtain the pressure in the sound field, it is now necessary to refer to the calibration of the 3A hydrophone shown in Figure 1. This calibration is in terms of db vs 1 volt. The computed level at the hydro- phone must, therefore, be changed into these terms. This correction is as follows: When the power dissipated in a 135-ohm resistance is lO-i*^ watt, the voltage e across tliat resistance is given by the relation 135 = 10-18 so that e--^ = 135 X 10-i«. On a decibel basis relative to 1 volt, this gives 201oge = 101og(135) - 160 = dbvs 1 volt. ,,w ,^AV P0WER»I60 VSIO
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